NAME
Net::Spooler - A Perl extension for writing spooling daemons
SYNOPSIS
# Create a subclass of Net::Spooler
use Net::Spooler;
package MySpooler;
@MySpooler::ISA = qw(Net::Spooler);
# Inherit everything, except a single method:
sub ProcessFile {
my $self = shift; my $file = shift;
# Try to process the file here
# Raise an exception, if something went wrong:
die "Failed: $!" unless Something();
# Return to indicate sucess.
}
# Create and run the spooler
package main;
my $spooler = Net::Spooler->new(
'spool-dir' => '/var/myspooler'
);
$spooler->Bind();
DESCRIPTION
This package contains a spooling daemon, in other words a process, that accepts files from an outside source (currently a Unix or TCP/IP socket), stores them in a spooling directory and processes them.
The package is implemented as an abstract base class: It is not usefull in itself, but you can get your spooling daemon easily by deriving a concrete subclass from `Net::Spooler'. In the best case you can inherit everything and overwrite just a single method, the ProcessFile method, which attempts to process a single file from the spooling directory.
`Net::Spooler' is in turn derived from the `Net::Daemon' package, thus it borrows class design, in particular methods and attributes, from `Net::Daemon'. See the Net::Daemon manpage for details on this superclass.
However, there are a few additions to `Net::Daemon':
Attributes
Like in `Net::Daemon', attributes can be set via the command line, in the config file or as constructor arguments (order descending from most important). And remember, that you can use the `Net::Daemon' attributes too! See the Net::Daemon manpage.
admin (B<--admin=<email>)
The administrators email address. From time to time it
may happen, that the admin receives an email in case of
problems.
expiretime (--expiretime=<time>)
If processing a file fails repeatedly, the file may
finally expire. This means that the file will be removed
from the spool directory and a message is sent to the
administrator.
The default value are 432000 seconds (5 days). A value
of 0 means that expiration never happens.
Example: Expire after 3 days.
--expiretime=259200
maxsixe (--maxsize=<maxsize>)
By default the maximum size of a file is restricted to
100000 bytes and larger files will be rejected. This
option is changing the size, a value of 0 means
disabling the limitation.
Example: Disable max size
--maxsize=0
processtimeout (--processtimeout=<timeout>)
If processing a single file may result in an endless
loop, or simply run too long, then you may specify a
timeout. The daemon will raise a signal after the given
amount of seconds and stop processing the file, as if
the method `ProcessFile' raised an exception.
The default value is 0 seconds which means that no
timeout is used.
Example: Use a timeout of 30 seconds.
--processtimeout=30
loop-timeout (--loop-timeout=<time>)
If processing a file failed, the spooler will reprocess
the file later by forking a child process after the
given amount of seconds, by default 300 seconds (5
minutes). This child process will run through all
scheduled file
spool-dir (--spool-dir=<dir>)
If the daemon accepts files, they are stored in the
spool directory. There's no default, you must set this
attribute.
Example: Use /var/myspooler as a spool directory.
--spool-dir=/var/myspooler
tmpfiles
This attribute is for internal use only. It contains an
hash ref, the keys being temporary file names to be
removed later.
Methods
As already said, the `Net::Spooler' package inherits from `Net::Daemon'. All methods of the superclass are still valid in `Net::Spooler', in particular access control and the like. See the Net::Daemon manpage for details.
Processing a file
$self->ProcessFile($file)
(Instance method) Called for processing a single file.
This is typically the only method you have to overwrite.
The method raises an exception in case of errors. If an
exception is raised, the scheduler will later retry to
process the file until it expires. See the queuetime
and expiretime attributes above.
If processing a file exceeds the processtimeout (see
above), then the scheduler will cancel processing the
method and continue as if it raised an exception. (This
timeout can be disabled by setting it to 0, the default
value.)
If the method returns without raising an exception, then
the scheduler assumes that the file was processed
successfully and remove it from the spool directory.
Choosing file names
my $sfile = $self->SequenceFile();
my $seq = $self->Sequence($sfile);
my $dfile = $self->DataFile($seq);
my $cfile = $self->ControlFile($seq);
(Instance methods) If the daemon receives a new file, it
has to choose a name for it. These names are constructed
as follows:
First of all, a so-called sequence number is generated
by calling the method Sequence. By default these are
the numbers 1, 2, 3, ... in 8 hex digits (00000001,
00000002, 00000003, ...). The last generated sequence
number is always stored in the sequence file (by default
$spool-dir/.sequence, set by calling the SequenceFile
method).
Two files are generated for processing the file: The
data file is the unmodified file, as received by the
client. The control file contains information used
internally by `Net::Spooler', for example the time and
date of spooling this file. By default the names $spool-
dir/$seq.dat and $spool-dir/$seq.ctl are used, generated
by calling the methods DataFile and ControlFile.
Temporary file names are derived by adding the suffix
.tmp.
Typically you rarely need to overwrite these methods.
Accepting a file from the client
$self->ReadFile($socket, $fh, $file, $control);
(Instance method) This method is actually reading the file $file from the socket $socket. The file is already opened and the method must use the file handle $fh for writing into $file. (The file name is passed for creating error messages only.)
The method may store arbitrary data in the hash ref $control: This hash ref is stored in the control file later.
The default implementation is accepting a raw file on the socket. You should overwrite the method, if you are accepting structured data, for example 4 bytes of file size and then the raw file. However, if you do overwrite this method, you should consider the maxsize attribute. (See above.)
A Perl exception is raised in case of problems.
Creating the control file
$self->ControlFile($fh, $file, $control);
(Instance method) Creates the control file $file by writing the hash ref $control into the open file handle $fh. (The file name $file is passed for use in error messages only.)
The default implementation is using the `Data::Dumper' module for serialization of $control and then writing the dumped hash ref into $fh.
A Perl exception is raised in case of problems; nothing is returned otherwise.
Reading the control file
my $ctrl = $self->ReadControlFile($file);
(Instance method) This method reads a control file, as created by the ControlFile method and creates an instance of Net::Spooler::Control.
The default implementation does a simple require (in a Safe compartment for security reasons, see the the Safe manpage package for details) for loading the hash ref from the file. The hash ref is then blessed into the package corresponding to $self: The package name of $self is taken by appending the string ::Control.
The method returns nothing, a Perl exception is thrown in case of trouble.
AUTHOR AND COPYRIGHT
This package is
Copyright (C) 1999 Jochen Wiedmann
Am Eisteich 9
72555 Metzingen
Germany
E-Mail: joe@ispsoft.de
All rights reserved.
You may distribute under the terms of either the GNU General Public License or the Artistic License, as specified in the Perl README file.
SEE ALSO
L<Net::Daemon(3)>